Plateau phase has been achieved in 64% of all newly diagnosed patients with multiple myeloma treated with the ABCM (adriamycin, BiCNU, cyclophosphamide and melphalan) regimen in the Medical Research Council (MRC) trials; this stable clinical stage of the disease is associated with no more than minimal symptoms. Several studies have found that α‐interferon (α‐IFN) maintenance therapy increases the duration of plateau phase, but it is less clear if this translates into prolonged survival. We report the effect of α‐IFN on the duration of plateau phase and overall survival in a trial with 284 patients who were randomized to receive α2b‐IFN (Intron‐A) or no maintenance therapy during first plateau phase. The minimum follow‐up after randomization was 21 months. There was no significant difference in the overall survival between the two treatment groups (χ2 = 0.32, P = 0.57). There was a trend towards longer relapse‐free survival in the patients allocated α‐IFN, but this trend to longer plateau phase was not statistically significant (χ2 = 1.62, P = 0.2). Disease progression at relapse on α‐IFN appears to be more severe with greater elevations from plateau levels of serum paraprotein (P = 0.06) and β2‐microglobulin (P = 0.03) levels. Physicians tended to start chemotherapy sooner after diagnosis of relapse when patients had received α‐IFN (P = 0.16). Although, in common with most other studies, there is a trend for patients treated with α‐IFN to have a longer plateau phase, this is counteracted by morbidity attributable to the treatment and a somewhat shortened survival post relapse. Meta‐analysis of interferon trials is required to assess whether the minor trend for longer survival in patients maintained on α‐IFN found in some studies is significant and, if so, the extent of this advantage.